1. Technical Field
This invention relates generally to the field of contactless battery chargers for portable devices, and more particularly to a contactless charger with an alignment indicator to facilitate efficient charging.
2. Background Art
Contactless, or inductive, electrical connections are well known in the field of portable electrical devices. For example, portable, motorized toothbrushes typically contain a rechargeable battery which is charged by an inductive connection. Similarly, portable wireless communication devices, such as two-way RF radios, cellular phones, paging devices, and wireless communicators, commonly utilize a rechargeable battery that, in certain applications, is recharged by contactless, induction charging.
Most all contactless chargers charge batteries by induction. Current, passed through a coil, creates a magnetic flux in accordance with Ampere's law. When a second coil is placed in close proximity to such a current-driven coil, the flux couples to the second coil, thereby “inducing” a current in the second coil. Such an induction circuit is illustrated in FIG. 1.
Turning now to FIG. 1, an inductively coupled charging system 10 has a primary side or base device 12 and a secondary side or portable device 16. A primary controller used as a primary charging device 11 as would be well known to one of ordinary skill in the art, is shown connected to the AC power source and to a primary coil 13. The primary coil 13 is shown inductively coupled to secondary coil 15 by field 14. The secondary coil 15 is coupled to battery 21 through a secondary charging device which is shown in this example as a rectifier circuit 19. The battery 21 in turn is connected to the load shown as RL 23. As would be well known to one of ordinary skill in the art, the energy coupled from the primary coil 13 is applied through the secondary coil 15 to charge the battery 21.
One problem that plagues most contactless chargers is aligning the secondary coil with the primary coil so as to couple the most magnetic flux to the secondary, thereby ensuring the most efficient charging process. One prior art solution for aligning the primary coil and secondary coil is to make a charger with a pocket having an encapsulated contactless plug, such that when an electronic device is placed in the pocket, the contactless plug fits within the device and aligns the primary coil with the secondary coil. This is referred to as a “lock and key” solution, in that the encapsulated plug serves as a “key” that fits into a recess in the device, which serves as the “lock”. Such a charger is taught in U.S. Pat. No. 5,952,814, entitled “Induction Charging Apparatus and an Electronic Device”, and is shown generally in FIG. 2.
The problem with the lock and key solution is that a unique charger must be specifically designed for each electronic device. Since every electronic device has a unique shape or form factor, manufacturers must make unique chargers to accommodate all of their different products. This specialization of chargers makes the product time consuming to design and expensive to manufacture.
Accordingly, there is a need for an improved, contactless charging system that facilitates alignment of the primary and secondary coils.